If you think this command is mainly about bad language, you are mistaken--it is primarily about vows and oaths that you take in God’s name that you do or don’t keep. In the ancient near east, and even up to today, a Vow is something that we promise to the Lord in His name and for the glory of his name, (such as your wedding vows) and an oath is using God’s name for asserting the truth of something to some other human being, like testifying in court.
What happens when you take a vow or oath in God’s name, and then you break it? You bring great dishonor to the name of God. I am going to bring up two ancient and modern examples which applied to Israelites and Americans: your marriage vow, and your church membership vow, which were taken in God’s name.
In Prayer Today:
Pray for the hallowing (sanctifying, glorifying) of God's name.